Protected Silver Nanoclusters Research Articles

Singlet oxygen generation efficiency and antimicrobial ability in glutathione protected Ag31 nanoclusters

Ligand protected silver nanoclusters (Ag NCs) have recently been reported to have significant applications as antimicrobial agents. In the current study, glutathione (SG) protected silver nanocluster was synthesized leading to Ag31SG19 by cyclic reduction and oxidative condition and was evaluated for its singlet oxygen generation and antibacterial activity. From the results of the study, Ag31SG19 was found to have inhibitory activity against Escherichia coli and Staphylococcus aureus with a diameter of 15.30 ± 0.58 mm and 16.70 ± 0.58 mm respectively. The Minimum Inhibitory Concentration was also calculated to have 0.3125 mg/ml and 0.1562 mg/ml respectively. In addition, the Ag31SG19 was found to have high efficiency for the generation of singlet oxygen. Based on the results of the study, the antimicrobial mechanisms of Ag31SG19 could be predicted to be mainly because of the generation of singlet oxygen species in addition to the activity due to the release of Ag+ ions from the nanoclusters. These multimechanistic antimicrobial effects make the synthesized Ag31SG19 to be a promising candidate for a broad range of antimicrobial applications.

Theoretical studies of the N-heterocyclic carbene ligand protected Ag29 clusters

The structure and bonding properties of N-heterocyclic carbene (NHC) protected silver nanoclusters were explored by Density Functional Theory (DFT) calculations. Based on the calculation studies of energy, bond order, and optical properties of these NHC-stabilized Ag clusters, NHC-VI exhibited the best substituted effect in these Ag clusters. These theoretical calculation results of NHC-stabilized atomically precise Ag clusters give new insight into the stabilization mechanism of these clusters and would help the construction of NHC-stabilized Ag clusters in experiments.

Covalently anchoring silver nanoclusters Ag44 on modified UiO-66-NH2 with Bi2S3 nanorods and MoS2 nanoparticles for exceptional solar wastewater treatment activity

For the first time, covalently anchoring size selected silver nanoclusters [Ag44(MNBA)30] on the Bi2S3@UiO-66-NH2 and MoS2@UiO-66-NH2 heterojunctions were constructed as novel photocatalysts for photodegradation of methylene blue (MB) dye. The anchoring of Ag44 on MoS2@UiO-66-NH2 and Bi2S3@UiO-66-NH2 heterojunctions extended the light absorption of UiO-66-NH2 to the visible region and improved the transfer and separation of photogenerated charge carriers through the heterojunctions with a unique band gap structure. The UV–Vis-NIR diffuse reflectance spectroscopic analysis confirmed that the optical absorption properties of the UiO-66-NH2 were shifted from the UV region at 379 nm to the visible region at ~ 705 nm after its doping with Bi2S3 nanorods and Ag44 nanoclusters (Bi2S3@UiO-66-NH-S-Ag44). The prepared Bi2S3@UiO-66-NH-S-Ag44 and MoS2@UiO-66-NH-S-Ag44 photocatalysts exhibited exceptional photocatalytic activity for visible light degradation of MB dye. The photocatalysts exhibited complete decolorization of the MB solution (50 ppm) within 90 and 120 min stirring under visible light irradiation, respectively. The supper photocatalytic performance and recycling efficiency of the prepared photocatalysts attributed to the covalent anchoring of the ultra-small silver clusters (Ag44) on the heterojunctions surface. The X-ray photoelectron spectroscopic analysis confirmed the charge of the silver clusters is zero. The disappearance of the N–H bending vibration peak of primary amines in the FTIR analysis of Bi2S3@UiO-66-NH-S-Ag44 confirmed the covalent anchoring of the protected silver nanoclusters on the UiO-66-NH2 surface via the condensation reaction. The Bi2S3@UiO-66-NH-S-Ag44 catalyst exhibited excellent recyclability efficiency more than five cycles without significant loss in activity, indicating their good potential for industrial applications. The texture properties, crystallinity, phase composition, particle size, and structural morphology of the prepared photocatalysts were investigated using adsorption–desorption N2 isotherms, X-ray diffraction (XRD), HR-TEM, and FE-SEM, respectively.

A turn on fluorescent method for the detection of ferric ions based on the size effect of silver nanoclusters

A fluorescence enhancement method is developed for the detection of ferric ions based on the bovine serum protein -protected silver nanoclusters. The fluorescence intensity of silver nanoclusters is greatly dependent on their size. Furthermore, silver clusters can be oxidized in the presence of ferric ions to form silver ions, which results in a change in the fluorescence intensity due to formation of small nanoclusters. Among them, the silver clusters with 30 silver atoms show weak original fluorescence intensity and can be used to detect ferric ions based on enhancement of fluorescence. The proposed fluorescent method exhibits an excellent linear range of 2 × 10−8−5 × 10−5 M, with a detection limit of 10 nM. This strategy shows good potential for the detection of ferric ions in food and environmental samples.

Heterocyclic thiol protected supramolecular self-assembly of silver nanoclusters for ultrasensitive detection of toxic Hg (II) ions in nanomolar range

Supramolecular self-assembly of heterocyclic thiolate protected silver nanoclusters (AgNCs) formed via non-covalent binding interactions exhibits a unique physicochemical property. Herein we demonstrate a facile synthesis of 2-mercaptobenzothiazole (MBT) protected self-assembled AgNCs (SA-AgNCs) in acetone–water medium. The existence of hydrophobic and bridging type coordination interactions describes the direct formation of SA-AgNCs. The photo stability of as obtained SA-AgNCs at 630 nm with orange emission is attributed to the cumulative electron-hole hopping interactions of individual Agn(MBT)m clusters present in supramolecular network of SA-AgNCs. The synergetic effect of self-assembly induced emission (SAIE) and ligand–metal-metal charge transfer (LMMCT) interactions of SA-AgNCs leads to the enhancement of photoluminescence properties. The SA-AgNCs serves as a fluorescent turn-off probe for the ultrasensitive detection of toxic Hg(II) ions at nanomolar ranges of 3.5–100 nM via quenching dynamics resulting from the metallophilic affinity of Hg2+-Ag+ ions. The favourable mechanism for the quenching dynamics was validated from the spectroscopic studies, that reveals as the Hg2+ ions approaches SA-AgNCs network, the combined effect of Hg2+-Ag+ alloying property and the detachment of Agn(MBT)m staple motifs from core silver clusters decreases the luminescence proportionality. The real sample analysis for the detection of Hg2+ ions in tap water and lactating mother’s milk samples were found satisfactorily.

Green Synthesis of Fluorescent Ag Nanoclusters for Detecting Cu2+ Ions and Its “Switch-On” Sensing Application for GSH

Herein, we prepared the L-histidine- (His-) protected silver nanoclusters (Ag NCs) by the microwave synthesis method. The synthesis process was rapid, facile, and environmentally friendly. Under 356 nm excitation, the as-prepared Ag NCs exhibited the blue fluorescence, and the fluorescence emission peak was located at 440 nm. The Ag NCs could successfully detect trace copper (Cu2+) ions in the aqueous solution and the limit of detection (LOD) was as low as 0.6 pM. Interestingly, the Ag NCs showed a different pH-dependent selectivity for both Cu2+ and iron (Fe3+) ions with no responses to other heavy metal ions. Furthermore, the as-fabricated fluorescent sensing system was utilized to detect glutathione (GSH, the LOD was 0.8 nM) by using the “switch-on” fluorescence recovery of Ag NCs through adding glutathione (GSH) to the Cu2+-Ag NCs solution.

Synthesis of highly stable fluorescent poly(methacrylic acid-co-itaconic)-protected silver nanoclusters and sensitive detection of Cu2.

Stable fluorescent silver nanoclusters (AgNCs) were synthesized through one-step UV photoreduction using the multiple carboxyl copolymer poly(methacrylic acid-co-itaconic acid) P(MAA-co-IA) as a novel template. The fluorescence lifetime and the quantum yield of the obtained AgNCs were 1.84 ns and 8.9% in an aqueous solution, respectively. Owing to the multiple carboxyls of the protective P(MAA-co-IA) template, the obtained AgNCs have excellent advantages such as good dispersity, and high stability, which make them suitable for highly sensitive and selective detection of Cu2+ by fluorescence quenching. A good linear relationship exists between the degree of fluorescence quenching for silver nanoclusters and Cu2+ concentration ranging from 0 to 10 μM. The limit of detection (LOD) is 6.36 nM. The result implies that the as-synthesized AgNCs show great potential in the analysis field.

Ratiometric fluorescence detection of dopamine based on effect of ligand on the emission of Ag nanoclusters and aggregation-induced emission enhancement

For small size metal nanoclusters, it is expected that template ligand will play an essential role in regulating the properties and structure. Using histidine (His) templated Ag nanoclusters and glutathione (GSH) and dihydrolipoic acid (DHLA) protected silver nanoclusters as models, due to the different electron donating abilities of different ligands, two silver nanoclusters with similar sizes have fluorescence emission peaks at different wavelengths. Furthermore, dopamine (DA) is a good electron donor, but is easily oxidized to dopaquinone, which can act as an electron accepter. Therefore, with addition of DA, which is easily oxidized by dissolved oxygen, the fluorescence of His-Ag nanoclusters quenches. Meanwhile, the ligands of GSH-DHLA-Ag nanoclusters contain sulfhydryl group, which has stronger reducing ability and stronger electron donating ability. Therefore, even in the presence of dopaquinone, the electron-donating effect of the ligand of the GSH-DHLA-Ag nanoclusters on the metal cores does not decrease significantly. Moreover, the addition of DA causes a certain degree of aggregation of GSH-DHLA-Ag nanoclusters, and the fluorescence intensity is enhanced due to the aggregation-inducing emission enhancement effect. Based on two types of silver nanoclusters, a ratiometric fluorescent sensor for DA analysis has been established. The linear range is 0−800 nM, and the limit of detection based on 3δ/s is 10 nM.

Turn-on fluorescence detection of cysteine with glutathione protected silver nanoclusters

In this work, we report a sensitive and selective turn-on fluorescence detection of cysteine with glutathione protected silver nanoclusters (GSH-Ag NCs). The glutathione stabilized silver nanoclusters were synthesized by the boiling water method. When excited at 380 nm, the GSH-Ag NCs exhibited a weak emission at about 680 nm, which could be enhanced by cysteine. The proposed method allows evaluation of cysteine in the range of 2–3000 μM with a detection limit of 0.51 μM. The recoveries were found to be 95.07%-101.38% when detecting cysteine contents in fetal bovine serum samples. In addition, we also discussed the possible mechanism for the fluorescence enhancement of GSH-Ag NCs by addition of cysteine. It might be the formation of cysteine and glutathione co-capped Ag NCs. This work reported a fluorimetric method for the assay of cysteine and provided a strategy for the synthesis of dual ligand-protected Ag nanoclusters.

A New Phase Transfer Strategy to Convert Protein-Capped Nanomaterials into Uniform Fluorescent Nanoclusters in Reverse Micellar Phase.

A new phase transfer strategy to convert aqueous phase protein-protected nanomaterials into fluorescent nanoclusters in the reverse micellar environment is introduced using bovine serum albumin (BSA)-protected silver nanoclusters (AgNCs) and nanoparticles (AgNPs) as an example. The basic pH employed in the fabrication of protein-protected nanoclusters induces the the protein capping to be negatively charged and facilitates the transfer process of the nanomaterials from aqueous phase to a cationic gemini surfactant (16-2-16)/hexane/hexanol/water reverse micelle (RM) phase. The original fluorescence characteristics of the seed nanocluster is retained after the transfer process. Strikingly, when both the nanomaterials (AgNCs and AgNPs) coexist in the aqueous feed solution, they are exclusively converted into uniform nanoclusters in the RM extract with enhanced fluorescence intensity.

Polyethyleneimine protected silver nanoclusters luminescence probe for sensitive detection of cobalt (II) in living cells

A simple luminescence sensor, based on polyethyleneimine protected silver nanoclusters (AgNCs@PEI) is successfully fabricated via one-pot reduction method. The obtained AgNCs@PEI are characterized by high-resolution transmission electron microscopy (HR-TEM), Dynamic light scattering (DLS), transient and steady-state fluorescence, and UV–vis spectroscopy. The NCs show large Stocks-shift (∼130nm), high tolerability to extreme pH and high ionic strengths, and excellent photo-stability under UV irradiation, laying the basement for the practical applications. In addition, the sensor is used to detect the Co2+ basing on the luminescence quenching, which is interfered by pH conditions (from pH4.0 to pH7.4). As a luminescence probe for Co2+ ions, the detection limit of AgNCs@PEI is as low as 0.25nM, which is much lower than that of many other reports. Additionally, the AgNCs@PEI possess the advantages of good selectivity, fast response and abroad linear detection. A linear response range in 0.5nM–50μM is achieved for Co2+ when using 20μM AgNCs@PEI in BR buffer solution (neutral condition pH7.4). Incubation time of AgNCs@PEI toward Co2+ is only 2min and it can distinguish Co2+ from other 13 metal ions. Furthermore, the probe (AgNCs@PEI) is applied to sensing and imaging of HeLa cells, showing low cytotoxicity and good sensitivity.

Hydroxyl radical induced chemiluminescence of hyperbranched polyethyleneimine protected silver nanoclusters and its application in tea polyphenols detection

Selective tea polyphenols detection based on hydroxyl radical induced chemiluminescence of hyperbranched polyethyleneimine protected silver nanoclusters is presented.

Antimicrobial Silver Nanoclusters Bearing Biocompatible Phosphorylcholine-Based Zwitterionic Protection.

Infection is one of the most serious issues in medical treatments leading to the development of several antimicrobial agents. In particular, silver ions released from silver substrates is well-known as a reliable antimicrobial agent that either kills the microorganisms or inhibits their growth. Unfortunately, many reports have shown that silver-based antimicrobial agents are toxic for human cells as well. To improve the biocompatibility of silver antimicrobial agents, we have synthesized thiol-terminated phosphorylcholine (PC-SH)-protected silver nanoclusters (PC-AgNCs) via strong thiol-metal coordination with controlled ultrasmall size of the clusters. A change in plasmon-like optical absorption was studied to affirm the successful synthesis of small thiolated AgNCs through the absorption spectra that become molecular-like for the AgNCs. We observed that PC-AgNCs were spherical with an average diameter of <2 nm. The ultrasmall size clusters were exceedingly immobilized by the PC-SH on the surface, resulting in excellent biocompatibility and antibacterial activity simultaneously. The biocompatible, antimicrobial PC-AgNCs exhibit interesting advantages compared with other silver antimicrobial agents for medical applications.

Enantioselective silver nanoclusters: Preparation, characterization and photoluminescence spectroscopy

Herein, we report a new wet-synthesis method to separate some water-soluble chiral silver nanoclusters with high yield. The cluster material was obtained by the reduction of silver nitrate with NaBH4 in the presence of three ligands l-penicillamine (l-pen), d-penicillamine (d-pen) and racemic mixture of penicillamine (rac-pen), functioning as capping ligand. For characterizing all silver cluster samples, the particle size was assessed by transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) and their average chemical formula was determined from thermogravimetric analysis (TGA) and elemental analysis (EA). The particles sizes of all three clusters are 2.1 ± 0.2 nm. The optical properties of the samples were studied by four different methods: UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), photoluminescence spectroscopy (PL) and circular dichroism (CD) spectroscopy. The spectra are dominated by the typical and intense plasmon peak at 486 nm accompanied by a small shoulder at 540 nm. Infrared spectroscopy was measured for the free ligand and protected silver nanoclusters, where the disappearance of the S-H vibrational band (2535–2570 cm−1) in the silver nanoclusters confirmed anchoring of ligand to the cluster surface through the sulfur atom. PL studies yielded the fluorescent properties of the samples. The main focus of this work, however, lies in the chirality of the particles. For all silver clusters CD spectra were recorded. While for clusters capped with one of the two enantiomers (D- or L-form) typical CD spectra were observed, no significant signals were detected for a racemic ligand mixture. Furthermore, silver clusters show quite large asymmetry factors (up to 3 × 10−4) in comparison to most other ligand protected clusters. These large factors and bands in the visible range of the spectrum suggest a strong chiral induction from the ligand to the metal core. Textural features of the prepared silver nanoclusters were investigated using nitrogen adsorption-desorption at −196 °C. Specific surface area SBET, pore volume and average pore diameter were calculated.

Silver nanoclusters as fluorescent nanosensors for selective and sensitive nitrite detection

Selective and sensitive fluorescence detection of nitrite through nitrite/H2O2 induced aggregation of hyperbranched polyethyleneimine protected silver nanoclusters.

A sensitive detection of Cr(vi) in wide pH range using polyethyleneimine protected silver nanoclusters

A sensitive fluorescence probe of polyethyleneimine protected silver nanoclusters (AgNCs@PEI) was proposed for the detection of trace level of Cr(vi) in both acidic and alkaline conditions.

One-pot one-cluster synthesis of fluorescent and bio-compatible Ag14 nanoclusters for cancer cell imaging.

Small-molecule-protected silver nanoclusters have smaller hydrodynamic diameter, and thus may hold greater potential in biomedicine application compared with the same core-sized, macromolecule (i.e. DNA)-protected silver nanoclusters. However, the live cell imaging labeled by small-molecule-protected silver nanoclusters has not been reported until now, and the synthesis and atom-precise characterization of silver nanoclusters have been challenging for a long time. We develop a one-pot one-cluster synthesis method to prepare silver nanoclusters capped with GSH which is bio-compatible. The as-prepared silver nanoclusters are identified to be Ag14(SG)11 (abbreviated as Ag14, SG: glutathione) by isotope-resolvable ESI-MS. The structure is probed by 1D NMR spectroscopy together with 2D COSY and HSQC. This cluster species is fluorescent and the fluorescence quantum yield is solvent-dependent. Very importantly, Ag14 was successfully applied to label lung cancer cells (A549) for imaging, and this work represents the first attempt to image live cells with small-molecule-protected silver nanoclusters. Furthermore, it is revealed that the Ag14 nanoclusters exhibit lower cytotoxicity compared with some other silver species (including silver salt, silver complex and large silver nanoparticles), and the explanation is also provided. The comparison of silver nanoclusters to state-of-the-art labeling materials in terms of cytotoxicity and photobleaching lifetime is also conducted.

Preparation and Spectroscopic Properties of Monolayer-Protected Silver Nanoclusters

Silver nanoclusters protected by 2-phenylethanethiol (1), 4-fluorothiophenol (2), and l-glutathione (3) ligands were successfully synthesized. The optical properties of the prepared silver nanoclusters were studied. The absorption signal of Ag@SCH2CH2Ph in toluene can be found at 469 nm, and Ag@SPhF in THF shows two absorption bands at 395 and 462 nm. Ag@SG in water absorbs at 478 nm. Mie theory in combination with the Drude model clearly indicates the peaks in the spectra originate from plasmonic transitions. In addition, the damping constant as well as the dielectric constant of the surrounding medium was determined. In addition, the CD spectra of silver nanoclusters protected by the three ligands (1–3) were also studied. As expected, only the clusters of type 3 gave rise to chiroptical activity across the visible and near-ultraviolet regions. The location and strength of the optical activity suggest an electronic structure of the metal that is highly sensitive to the chiral environment imposed by the glutathione ligand. The morphology and size of the prepared nanoclusters were analyzed by using transmission electron microscopy (TEM). TEM analysis showed that the particles of all three types of silver clusters were small than 5 nm, with an average size of around 2 nm. The analysis of the FTIR spectra elucidated the structural properties of the ligands binding to the nanoclusters. By comparing the IR absorption spectra of pure ligands with those of the protected silver nanoclusters, the disappearance of the S–H vibrational band (2535–2564 cm–1) in the protected silver nanoclusters confirmed the anchoring of ligands to the cluster surface through the sulfur atom. By elemental analysis and thermogravimetric analysis, the Ag/S ratio and, hence, the number of ligands surrounding a Ag atom could be determined.

Spectroscopic evidence of a bidentate-binding of meso-2,3-dimercaptosuccinic acid on silver nanoclusters

New insight into the metal–ligand binding interaction in meso-2,3-dimercaptosuccinic acid (DMSA) protected silver nanoclusters (NCs) is presented in this work. IR, Raman and 13C NMR spectroscopic characterizations and DFT calculations suggest that DMSA forms a bidentate binding, rather than the originally-proposed monodentate binding, via two sulfur atoms with the underlying Ag7 NC, which is in agreement with recent ab initio calculations.

212 POSTER A Phase I study of huC242-DM4 to assess the safety and pharmacokinetics of huC242-DM4 administered as a single intravenous infusion once every three weeks to subjects with solid tumors

New insight into the metal–ligand binding interaction in meso-2,3-dimercaptosuccinic acid (DMSA) protected silver nanoclusters (NCs) is presented in this work. IR, Raman and 13C NMR spectroscopic characterizations and DFT calculations suggest that DMSA forms a bidentate binding, rather than the originally-proposed monodentate binding, via two sulfur atoms with the underlying Ag7 NC, which is in agreement with recent ab initio calculations.